1. Field of the Invention
This invention relates to novel 2-nitroethylcyclopentane compounds having the formula (I) which are useful as intermediates for the synthesis of prostaglandin compounds.
2. Description of the Prior Art
It is well known that the naturally-occurring prostaglandin compounds are composed of 20 carbon atoms and contains in their structure a cyclopentanone ring and exist broadly in the brain, lung, kidney, semen, uterus membrane, etc. of living body. These prostaglandin compounds are also known to have a wide variety of excellent pharmacological activities such as anti-ulcer, hypotensive, anti-asthmatic, uterotonic activities depending upon critical differences in the chemical structure of the prostaglandin compounds, and recently the synthesis of prostaglandin compounds has been extensively studied.
Hitherto, in the synthesis of prostaglandin derivatives, the basic cyclopentanone structure is typically formed by (1) a method utilizing Dieckmann reaction as described, for example, in P. S. Pinkney, Org. Synthesis, Coll. Voll., 2, 116 (1943), (2) a method by Claisen condensation of 1,4-dicarbonyl compounds as described, for example, in R. A. Ellison, Synthesis, 397 (1973), (3) a method starting with cyclopentadiene as described, for example, in E. J. Corey et al., J. Amer. Chem. Soc. 93, 1489 (1971), (4) a method by ring-contracting procedure of cyclohexane derivatives as described, for example, in R. B. Woodward et al., J. Amer. Chem. Soc., 95, 6853 (1973) and (5) a method using a bicyclo[3.1.0]hexane compound as an intermediate as described, for example, in W. P. Schneider, Chem. Commun., 304 (1969) and E. J. Corey et al., J. Amer. Chem. Soc., 94, 4014 (1972).
Recently, various improved methods for the synthesis of prostaglandin compounds have been developed as described, for example, in G. Stork et al., J. Amer. Chem. Soc., 98, 1583 (1976) for the above method (1), and F. Johnson et al., J. Amer. Chem. Soc., 98, 1285 (1976) for the above method (2), but each of these conventional methods is not considered advantageous procedure from the standpoint of that it requires expensive and/or dangerous reagents, critical reaction conditions which are very difficult to control, and isolation and purification of the desired product with considerable difficulty, and that the method generally has low selectivity of reaction thereby resulting in low yield of the desired product.
Also, it is well known that lactol derivatives are very useful starting materials for the synthesis of prostaglandin compounds, as described in E. J. Corey et al., J. Amer. Chem. Soc., 91, 5675 (1969). The 2-nitroethylcyclopentane compounds of the formula (I) of the present invention can be converted into the above lactol derivatives by, for example, converting the nitroethyl moiety of the compounds into an aldehyde group, as described hereinafter.
Hitherto, various methods for preparing lactol derivatives or precursors therefor have been proposed. Typical examples of such methods are (1) a method starting with an adduct of cyclopentadiene obtained by Diels-Alder reaction, as described in E. J. Corey et al., J. Amer. Chem. Soc., 91, 5657 (1969), E. D. Brown et al., Chem. Commun., 642 (1974), and G. Jones et al., Chem. Commun., 609 (1972); 2) a method utilizing a ring-opening reaction of an epoxide derived from 1,4-dihydroxy-2-cyclopentene, as described in J. Fried et al., J. Amer. Chem. Soc., 94, 4343 (1972); (3) a method starting with dicyclopentadiene, as described in D. Brewster et al., Chem. Commun., 1235 (1972); (4) a method comprising solvolysis of a cyclopropane derivative, as described in, for example, R. C. Kelly et al., J. Amer. Chem. Soc., 95, 2746 (1973); (5) a method starting with cis-1,3,5-cyclohexanetriol, as described in R. B. Woodward et al., J. Amer. Chem. Soc., 95, 6853 (1973); (6) a method utilizing a ring-contracting reaction of a cyclohexene derivative, as described in E. J. Corey et al., Tetrahedron Lett., 3091 (1973); (7) a method starting with an adduct obtained by the Prins reaction between norbornadiene and formaldehyde or chloral, as described in R. Peel et al., Chem. Commun., 151 (1974) and S. Takano et al., J. Org. Chem., 42, 786 (1977), etc.
Each of these conventional methods has characteristic features, but generally, also has one or more disadvantages in that these methods comprises a number of reaction steps, require expensive or dangerous reagents and exhibit low steric selectivity and, therefore, appear to be unsatisfactory as industrial methods.